In a design of a large rotary module of a machine tool, the most important issue is whether or not a bearing assembly is able to provide a desired supporting force, so as to provide the rotary module with sufficient precision and rigidity. Nowadays, the so-called “three-piece bearing configuration” is normally used as the bearing assembly of a large rotary module.
Germany Patent No. DE4227366A1 and Germany Patent Application No. DE102005053622A1 disclosed a configuration of a three-piece roller bearing, such as an YRT turntable bearing, with a radial bearing and an axial bearing integrally disposed in a single set, wherein the three-piece roller bearing disclosed in Germany Patents No. DE4227366A1 basically only differs from that of No. DE102005053622A1 in the way of configuring the bearings, while both of them are able to serve as a bearing assembly for a large rotary module.
However, the manufacturing cost of the three-piece bearing configuration is very expensive, so that the machine tool manufacturers are still unable to reduce the manufacturing cost. Meanwhile, when users operate a large rotary module with the three-piece bearing configuration, they normally cannot accurately control the precision and rigidity of the large rotary module, in that the configuration of the radial bearing and the axial bearing of the large rotary module are designed to be integrally disposed in a single set.
In summary, it is an urgent problem in the art to be solved how to make a large rotary module having both higher precision and rigidity under a reasonably manufacturing cost.